What's wrong with my wav file?

[drapes]

Hi all,

First off, I'd like to thank everyone for this wonderful site. In the last couple of months I've managed to get myself set up with a sweet little stealth rig for very little $$. I did it all by lurking; searching and reading got me to an iRiver h120 and to Church Audio for some cardioids and an ST-9100 pre-amp. I got the iRiver through the Yard Sale in a great transaction and Chris Church has been very nice to me as well. I've used my setup a few times now and I'm astounded by how the recordings sound. This site is an awesome resource, thank you.

Now this is my first post; I've got a wav file that just doesn't look or sound right. Forgive me if I get the screen-shots f*cked up. The file names match the description if they are not visible in the post.

Please have a look at the wav form in the file wav_somethingswrong.gif. The bottom half is all wrong. I really don't know what I'm looking at when I look at these things, but for what it's worth, the scale is "Waveform" from 1.0 at the top to -1.0 at the bottom. The sound isn't great and there are crackles and snaps in the quiet bits.

The file wav_looksgood.gif is from the same song two nights earlier. Same scale; everything looks healthy.

Now I have a couple of guesses to follow up on:

1) 9v battery in the pre-amp. It had a maximum of 20 hours service before this show started and I thought it was supposed to last much longer than that.

2) Loose connection? Could a loose connection cause these symptoms?

Thank you everyone again,

drapes

P.S. If anyone is trying to guess; the song in the highlighted area of the screenshots is Black Sabbath's "Heaven and Hell". The good one is from Montreal on the 26th, and the not so good one is from Ottawa on the 28th.

[fozzy]

I would try replacing the 9v battery.  I do not know what folks are getting for runtime on the church preamps.  A batterybox w/o a pre will run for a very long time but introducing the preamp would increase the draw. 

did by chance you leave the preamp on between shows or idling for a long time before the show on the 28th.  10-15 hours may be a reasonable time to expect a single 9v to last.
What type of 9v are you using?
Did the waveform get worse as the show went on?
Do you have a multimeter available to check the voltage of the 9v that is in there now?

I know it isn't a accurate test but what do the waveforms look like doing a test recording of the stereo.

If all of the above checks out the pre > iriver connection may not have been 100%.  is there a difference between channels or is the sound identical?

+T to get you started, welcome to TS.com

[Alchemy]

For starters, it doesn't look like the DC offset in the "wav_somethingswrong.gif" screenshot is at zero.

[boojum]

P.S. If anyone is trying to guess; the song in the highlighted area of the screenshots is Black Sabbath's "Heaven and Hell". The good one is from Montreal on the 26th, and the not so good one is from Ottawa on the 28th.

Well, hell, man, everything is better in Montreal.  C'est vrai!  Bien sur!  Tabernacle!    B)

[drapes]

I would try replacing the 9v battery.  I do not know what folks are getting for runtime on the church preamps.  A batterybox w/o a pre will run for a very long time but introducing the preamp would increase the draw. 

did by chance you leave the preamp on between shows or idling for a long time before the show on the 28th.  10-15 hours may be a reasonable time to expect a single 9v to last.
What type of 9v are you using?
Did the waveform get worse as the show went on?

The bottom half of the waveform appears to move slowly upwards throughout the wav file.
It was an Energizer alkaline. My estimate of the usage time included idling between shows. I did two test runs at clubs plus a bit of fiddling around at home before the three concerts on the 26th, 27th, and 28th. The 26th and 27th sound fine but the 28th not so good. I'll test the current voltage and try a test with the stereo.

+T to get you started, welcome to TS.com

Thank you!

For starters, it doesn't look like the DC offset in the "wav_somethingswrong.gif" screenshot is at zero.

Thanks. I'm new at this and with a little Googling I think I can follow this idea. I guess it leaves the question: why? The previous two nights as well as my practices at the clubs looked great, but the third not so much. I'm focusing on the battery idea for now.

[Alchemy]

Thanks. I'm new at this and with a little Googling I think I can follow this idea. I guess it leaves the question: why? The previous two nights as well as my practices at the clubs looked great, but the third not so much. I'm focusing on the battery idea for now.

I would contact the person that built that preamp.

[Brennan]

I can't 100% explain what exactly the DC offset IS but I can say you can change it by dragging the right side of the screen up or down in Audacity (I think that's what you're using..?), and many other programs.

That was the first thing I thought of when I saw your screenshots.. +T btw

[drapes]

I can't 100% explain what exactly the DC offset IS but I can say you can change it by dragging the right side of the screen up or down in Audacity (I think that's what you're using..?), and many other programs.

That was the first thing I thought of when I saw your screenshots.. +T btw

Thanks!

I believe I can also run a Normalize effect that will reset the DC offset to 0.

I'll give all these things a try, for now I'm focusing on tweaking the best possible sound out of the recordings that went well and I'll return to this one when I get a little more experienced with Audacity.

[Brian Skalinder]

I believe I can also run a Normalize effect that will reset the DC offset to 0.

Doesn't look like a DC offset problem to me.  If it was DC offset, the (+) and (-) peaks would roughly mirror one another, as in the "good" screenshot, rather than the very lopsided "bad" screenshot.  With a DC offset problem, the waveform would still look like the "good" screenshot, but horizontal center line is simply offset to a value other than "0".  Only time I had a waveform look anything like that, one of the op amps in my modSBM-1 had fried.

Are you able to replicate the problem in a controlled test environment?

I'd suspect the preamp, based on my previous experiences, but...strongly recommend contacting Chris Church directly as he may not see this post.

[drapes]

An update...

1) I tested the voltage in the 9v battery and it's below nominal: 8.24v on my digital multimeter. A brand new battery gave a reading of 9.31v.
2) I did a quick test with the stereo but it was inconclusive. Not enough volume I guess. I may need to try again when noone else is home and get the knob cranked. Even then I'm not sure if it will be loud enough.

But, it would seem the battery is the very likely culprit. I've PM'd Chris Church about this.

thanks all,

drapes

[jeromejello]

An update...

1) I tested the voltage in the 9v battery and it's below nominal: 8.24v on my digital multimeter. A brand new battery gave a reading of 9.31v.
*snip*
But, it would seem the battery is the very likely culprit. I've PM'd Chris Church about this.

i dont know if i would for sure say it was the battery.  aside from 8.24v being awfully close to full power; the only time i have had issues when it was the battery that caused it you could see it in the wave form, it would affect both the top and the bottom and lower the gain gradually as the battery died out.

your wave form shows only the bottom being affected...

fwiw, i am basing my experience on both a battery box (spsb-7) and sd mp-2.  i have no hands on info to share in regards to church products.

[Church-Audio]

Hi all,

First off, I'd like to thank everyone for this wonderful site. In the last couple of months I've managed to get myself set up with a sweet little stealth rig for very little $$. I did it all by lurking; searching and reading got me to an iRiver h120 and to Church Audio for some cardioids and an ST-9100 pre-amp. I got the iRiver through the Yard Sale in a great transaction and Chris Church has been very nice to me as well. I've used my setup a few times now and I'm astounded by how the recordings sound. This site is an awesome resource, thank you.

Now this is my first post; I've got a wav file that just doesn't look or sound right. Forgive me if I get the screen-shots f*cked up. The file names match the description if they are not visible in the post.

Please have a look at the wav form in the file wav_somethingswrong.gif. The bottom half is all wrong. I really don't know what I'm looking at when I look at these things, but for what it's worth, the scale is "Waveform" from 1.0 at the top to -1.0 at the bottom. The sound isn't great and there are crackles and snaps in the quiet bits.

The file wav_looksgood.gif is from the same song two nights earlier. Same scale; everything looks healthy.

Now I have a couple of guesses to follow up on:

1) 9v battery in the pre-amp. It had a maximum of 20 hours service before this show started and I thought it was supposed to last much longer than that.

2) Loose connection? Could a loose connection cause these symptoms?

Thank you everyone again,

drapes

P.S. If anyone is trying to guess; the song in the highlighted area of the screenshots is Black Sabbath's "Heaven and Hell". The good one is from Montreal on the 26th, and the not so good one is from Ottawa on the 28th.

From looking at the wav's I would say its a battery issue but, I could tell more with a sample. I think it could also be a distortion issue where was the gain level on the preamp? in relation to the gain on your IRIVER?

[drapes]

From looking at the wav's I would say its a battery issue but, I could tell more with a sample. I think it could also be a distortion issue where was the gain level on the preamp? in relation to the gain on your IRIVER?

I've attached a couple of short samples. The restriction in file size limits me to about 3 seconds of wav zipped up. Let me know if you need more and we can work something out.

For the recording that doesn't look so good I had the gain on the iRiver set at 4.5dB or so, and the gain knob on the 9100 at about a half way up I'd guess. The first two nights I had the gain on the iRiver at about 12 and the gain on the pre a little lower. These settings were all by accident although I did read somewhere on these forums that someone liked about 2/3 external gain, 1/3 iRiver gain so that's what I aimed for.

Funnily enough the one that looks worse still almost sounds better. I was so much better positioned and I had really hoped for a very nice recording.

[Church-Audio]

From looking at the wav's I would say its a battery issue but, I could tell more with a sample. I think it could also be a distortion issue where was the gain level on the preamp? in relation to the gain on your IRIVER?

I've attached a couple of short samples. The restriction in file size limits me to about 3 seconds of wav zipped up. Let me know if you need more and we can work something out.

For the recording that doesn't look so good I had the gain on the iRiver set at 4.5dB or so, and the gain knob on the 9100 at about a half way up I'd guess. The first two nights I had the gain on the iRiver at about 12 and the gain on the pre a little lower. These settings were all by accident although I did read somewhere on these forums that someone liked about 2/3 external gain, 1/3 iRiver gain so that's what I aimed for.

Funnily enough the one that looks worse still almost sounds better. I was so much better positioned and I had really hoped for a very nice recording.

How close were you to the PA and were you using the windscreens? It sounds like the diaphragm on my mic bottomed out... Or you should have used the High pass filter.. Its hard to say but it sounds like you were very close the the PA subwoofers.

[drapes]

How close were you to the PA and were you using the windscreens? It sounds like the diaphragm on my mic bottomed out... Or you should have used the High pass filter.. Its hard to say but it sounds like you were very close the the PA subwoofers.

I left the windscreens at home. Hard to judge but I was 50-60 feet from the PA, maybe more. The seating was quite steep so the PA was just out there hanging in front of me. I thought it would sound good.

The night before I was on the floor about 20 feet from the PA and it came out great. Same band different arena, and it felt like the sound was similar. The night before that I was a long way back. I listened to each recording in the morning prior to the next show and decided that I didn't need the high pass filter.